Blow-pipe structure

ABSTRACT

Provided is a blow-pipe structure for a blast furnace facility configured so as to be capable of suppressing slag adhesion by using a simple structure, even if pulverized coal with an unadjusted softening temperature is used. The blow-pipe structure is attached to a tuyere in a blast furnace main body that produces pig iron from iron ore. The blow-pipe structure injects auxiliary fuel pulverized coal together with hot air and slag from the pulverized coal containing a component that is melted by the hot air and/or heat from the combustion of the pulverized coal combustion heat. The blow-pipe structure has an internal/external double pipe structure having an internal pipe that continues from a header pipe that supplies the hot air, to the vicinity of the tuyere and opens, said internal pipe being provided inside an external pipe that continues from the header pipe to the tuyere.

TECHNICAL FIELD

The present invention relates to a blow-pipe structure for use with a blast furnace facility, and, in particular, to a blow-pipe structure that can be advantageously used to blow pulverized coal obtained by pulverizing low-grade coal into a furnace as an auxiliary fuel along with hot air.

BACKGROUND ART

A blast furnace facility is used to produce pig iron from iron ore by introducing feedstocks such as iron ore, limestone, coal, and the like into the interior of a main blast furnace body from the apex thereof, and injecting hot air and pulverized coal (PCI coal) as an auxiliary fuel through a tuyere located toward the bottom on a side of the furnace.

In a blast furnace facility of this sort, if low-grade coal generally having a low ash melting point of 1,100 to 1,300° C., such as sub-bituminous coal or lignite, is used as the pulverized coal during the operation of injecting pulverized coal, the oxygen contained in the roughly 1,200° C. hot air used to inject the pulverized coal into the furnace engages in a combustion reaction with part of the pulverized coal. The combustion heat generated thereby causes low-melting point ash (“slag”) to melt within the injection lance or tuyere.

The melted slag is rapidly cooled through contact with the tuyere, which is constantly cooled in order to protect it from the temperature of the blast furnace. As a result, solid slag adheres to the tuyere, leading to the problem of blockage in the blow pipe flow path.

In order to solve this problem, the softening point (temperature) of the slag within the pulverized coal is adjusted to a melting point that is equal to or greater than the temperature within the blast furnace if the slag has a low softening point, preventing slag from adhering to tuyeres, as, for example, in the conventional art disclosed in Patent Document 1 listed below.

Patent Document 2 listed below discloses an arrangement in which a divider ring is provided in a hollow section of a tuyere. The divider ring creates a two-layered pipe structure that divides the front end of the tuyere into a central region main channel and a peripheral region secondary channel, and gas supplied from a rear end of the tuyere is divided into streams passing through the main channel and the secondary channel, creating a jet in the furnace.

CITATION LISTS Patent Literatures

Patent Document 1: Japanese Unexamined Patent Application Publication No. H05-156330A

Patent Document 2: Japanese Unexamined Patent Application Publication No. H06-235009

SUMMARY OF INVENTION Technical Problem

However, attention has been called to the following two problems in the method according to the method of Patent Document 1 as described above.

The first problem is that it is difficult to completely (homogeneously) mix pulverized coal and additives, with the result that slag formation cannot be prevented at parts where the proportion of additive in the mixture is less than a predetermined value.

The second problem is that a new source of calcium oxide (CAA), such as limestone or serpentinite, is necessary, creating excessive costs.

Meanwhile, there is a region in which a two-layered pipe is not formed from the outlet of a lance to the divider ring in the conventional structure disclosed in Patent Document 2, with the result that at least some pulverized coal inevitably fails to enter into the divider ring and flows into the secondary channel in the peripheral region.

In view of these circumstances, there is a demand for a blow-pipe structure for use with blast furnace facilities that allows for the suppression of slag adhesion using a simple structure without the need for softening point adjustment.

The present invention was conceived in order to solve the problems described above, and has an object of providing a blast furnace facility blow-pipe structure that allows slag adhesion to be suppressed using a simple structure even if pulverized coal of an unadjusted softening point is used.

Solution to Problem

In order to solve the problem described above, the present invention employs the following means.

A blow-pipe structure according to an aspect of the present invention is a blow-pipe structure attached to a tuyere for a main blast furnace body that produces pig iron from iron ore, the blow-pipe structure injecting pulverized coal as an auxiliary fuel along with hot air, slag from the pulverized coal containing a component that is melted by the hot air and/or heat from the combustion of the pulverized coal, the structure being an internal/external double pipe structure in which an internal pipe that continues from a header pipe, which supplies the hot air, to the vicinity of a tuyere and opens is provided inside an external pipe that continues from the header pipe to the tuyere, and a pulverized coal outlet of an injection lance for introducing the pulverized coal opens to the interior of the internal pipe.

In accordance with this blow-pipe structure, an internal/external double pipe structure is provided in which an internal pipe that continues from a hot-air supplying header pipe to the vicinity of a tuyere and opens is provided within an external pipe that extends from the header pipe to the tuyere, and a pulverized coal outlet of an injection lance for introducing pulverized coal opens to the interior of the internal pipe, allowing the flow of pulverized coal introduced through the injection lance to be completely segregated from the wall of the external pipe, i.e., the inner wall of the blow pipe, on the upstream side of the tuyere. In addition, pulverized coal can be passed through the tuyere at a distance from the surface of the tuyere. This impedes the adhesion of pulverized coal slag to the surface of the tuyere or the inner wall of the blow pipe.

In the invention described above, it is preferable that a flow path resisting element be provided at a position in the flow path formed between the external pipe and the internal pipe and near the outlet of the internal pipe.

This allows for a greater flow rate within the internal pipe than within the external pipe. As a result, hot air flowing out of the external pipe flows in the direction of the center of the flow path, thus impeding the flow of the pulverized coal introduced into the internal pipe in the direction of the external pipe.

In the invention described above, it is preferable to provide a nitrogen injection pipe for supplying nitrogen into the internal pipe.

This allows the operating conditions of the internal pipe and the external pipe to be altered. In this case, nitrogen can be injected into the internal pipe to reduce the temperature of the hot air. As a result, the temperature of the hot air within the internal pipe can be adjusted to create an environment in which the pulverized coal cannot easily combust.

In the invention described above, it is preferable to provide an oxygen injection pipe for supplying oxygen into the external pipe.

This allows the operating conditions of the internal pipe and the external pipe to be altered. In this case, oxygen can be injected into the external pipe in order to allow for rapid combustion when the gases from the internal and external pipes are mixed immediately before the tuyere despite the environment unconducive to the combustion of the pulverized coal within the internal pipe.

Advantageous Effects of Invention

In accordance with the blow-pipe structure of the present invention described above, there is provided an internal/external double pipe structure in which an internal pipe is provided within an external pipe that continues from a hot air-supplying header pipe to a tuyere, and a pulverized coal outlet of an injection lance for introducing pulverized coal opens to the interior of the internal pipe, impeding the adhesion of pulverized coal slag to the surface of the tuyere or the inner wall of the blow pipe. This allows slag adhesion to be suppressed in the blow-pipe structure using a simple double pipe structure, even if softening point adjustment is not performed.

As a result, even low-grade coals having low ash melting points of 1,100° C. to 1,300° C., such as sub-bituminous coal or lignite, can be used as the pulverized coal constituting the auxiliary fuel by modifying the same for use as feedstock coal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of the axial direction of an embodiment of the blow-pipe structure according to the present invention.

FIG. 2 is an illustration of an example arrangement for a blast furnace facility to which the blow-pipe structure illustrated in FIG. 1 is applied.

DESCRIPTION OF EMBODIMENTS

An embodiment of the blow-pipe structure according to the present invention will now be described with reference to the drawings.

The blow-pipe structure according to the embodiment is used with a blast furnace facility in which pulverized coal of the low-grade coal constituting the feedstock coal is injected through a tuyere into a blast furnace along with hot air.

For example, in a blast furnace facility such as that illustrated in FIG. 2, feedstock 1 constituted by iron ore, limestone, and coal or the like is fed from a metered feedstock feeder 10 via a transport conveyor 11 into a furnace apex hopper 21 provided at the apex of a main blast furnace body 20. A plurality of tuyeres 22 is provided in a lower side wall of the main blast furnace body 20 at a roughly uniform pitch in the circumferential direction. Each of the tuyeres 22 is linked to a downstream end of a blow pipe 30 for feeding hot air 2 into the interior of the main blast furnace body 20. The upstream end of each of the blow pipes 30 is connected to a hot air feeder 40 constituting the source of the hot air 2 supplied to the interior of the main blast furnace body 20.

A pulverized coal producing device 50 that performs a pretreatment (modification) such as evaporating moisture in the coal out of the feedstock coal (sub-bituminous coal, lignite, or other low-grade coal), followed by pulverizing the low-grade coal to produce pulverized coal, is provided near the main blast furnace body 20.

Modified pulverized coal (modified coal) 3 produced by the pulverized coal producing device 50 is conveyed by a carrier gas 4, such as nitrogen gas, to a cyclone separator 60. The pulverized coal 3 conveyed by the gas is separated from the carrier gas 4 by the cyclone separator 60, after which the coal falls into and is stored in a storage tank 70. This modified pulverized coal 3 is used as blast furnace injection coal (PCI coal) for the main blast furnace body 20.

The pulverized coal 3 within the storage tank 70 is fed into an injection lance (hereafter, “lance”) 31 of the blow pipe 30 described above. The pulverized coal 3 combusts upon being fed into the hot air flowing through the blow pipe 30, producing a flame at the end of the blow pipe 30 and forming a raceway. This causes the coal or the like contained in the feedstock 1 being introduced into the main blast furnace body 20 to combust. As a result, the iron ore contained in the feedstock 1 is reduced, becomes pig iron (molten iron) 5, and is removed through a pig iron outlet 23.

Preferred properties of the pulverized coal 3 fed from the lance 31 into the blow pipe 30 as blast furnace injection coal, that is, of the modified pulverized coal (auxiliary fuel) formed by modifying and pulverizing low-grade coal, are an oxygen atom content (dry basis) of 10 to 18 weight %, and an average pore size of 10 to 50 nanometers (nm). A more preferable average pore size for the modified pulverized coal is 20 to 50 nanometers (nm).

In pulverized coal 3 having such properties, there is a large release of and reduction in tar-forming groups of oxygen-containing functional groups (carboxyl groups, aldehyde groups, ester groups, hydroxyl groups, etc.) but breakdown (reduction) of the main skeleton (the combustible component primarily formed from carbon, hydrogen, and oxygen) is greatly suppressed. Thus, when the coal is injected through the tuyeres 22 into the main blast furnace body 20 along with the hot air 2, the high oxygen atom content of the main skeleton and the large diameter of the pores not only facilitates dispersion of the oxygen in the hot air 2 into the coal, but also greatly impedes the generation of tar, allowing for complete combustion with almost no uncombusted carbon (soot) being produced.

In order to produce (modify) this pulverized coal 3, a drying step of heating (at 110 to 200° C. for 0.5 to 1 hours) and drying the sub-bituminous coal, lignite, or other low-grade coal (dry-basis oxygen atom content: greater than 18 weight %; average pore size: 3 to 4 nm) constituting the feedstock coal in a low-oxygen atmosphere having an oxygen concentration of 5 vol % or less is performed in the pulverized coal producing device 50.

After moisture is removed in the drying step described above, a dry distillation step in which the feedstock coal is reheated (at 460 to 590° C., preferably 500 to 550° C., for 0.5 to 1 hours) in a low-oxygen ambient atmosphere (oxygen concentration: 2 vol % or less) is performed. Dry distilling the feedstock coal in this dry distillation step removes generated water, carbon dioxide, and tar in the form of dry distillation gas or dry distillation oil.

The feedstock coal then proceeds to a cooling step in which the coal is cooled (to 50° C. or less) in a low-oxygen atmosphere having an oxygen concentration of 2 vol % or less, then pulverized (particle diameter: 77 μm or less (80% pass)) in a pulverization step.

In the embodiment, as illustrated, for example, in FIG. 1, the structure described hereinafter has been adopted for a blow pipe 30 that is attached to a tuyere 22 of a main blast furnace body 20 for producing pig iron from iron ore and injects pulverized coal 3 as an auxiliary fuel along with hot air 2, slag from the pulverized coal 3 containing a component that is melted by the hot air 2 and/or the heat from the combustion of the pulverized coal 3.

Specifically, the blow pipe 30 illustrated in the drawing has an internal/external double pipe structure. This internal/external double pipe structure continues from a header pipe 41, which is connected to a hot air feeder 40 and supplies hot air 2, to the tuyere 22 and features an internal pipe 30 b provided within an external pipe 30 a.

Specifically, the external pipe 30 a of the blow pipe 30 branches from the header pipe 41 and is connected to the tuyere 22. By contrast, the internal pipe 30 b of the blow pipe 30 branches from the header pipe 41, like the external pipe 30 a, and has a downstream internal pipe outlet 30 c which opens near an inlet of the tuyere 22.

The blow pipe 30 thus has an internal/external double pipe structure in which the internal pipe 30 b, which continues from the hot air 2-supplying header pipe 41 to near the tuyere 22 where an internal pipe outlet 30 c opens, is provided within the external pipe 30 a which continues from the header pipe 41 to the tuyere 22.

In other words, the blow pipe 30 has an internal/external double pipe structure in which an internal pipe 30 b for introducing pulverized coal 3 is concentrically provided within the external pipe 30 a constituting the main body of the blow pipe, segregating the flow paths.

The external pipe 30 a and internal pipe 30 b of the blow pipe 30 preferably have a cross-sectional area ratio of approximately 1:1. To give a specific example, if, for example, the inner diameter of the tuyere 22 is 160 mm, the inner diameter of the external pipe 30 a is 210 mm, and the inner diameter of the internal pipe 30 b is 140 mm.

In addition, the lance 31 for introducing the pulverized coal 3 into the blow pipe 30 passes through the external pipe 30 a and the internal pipe 30 b and has a pulverized coal outlet 31 a that opens to the interior of the internal pipe 30 b.

In a blow pipe 30 having an internal/external double pipe structure of this sort, pulverized coal 3 is introduced by the lance 31 into the interior of the internal pipe 30 b, allowing the flow of pulverized coal 3 to be completely segregated from the surface of the wall of the external pipe 30 a on the upstream side of the tuyere 22. That is, the flow of pulverized coal 3 is completely segregated from the surface of the inner wall of the blow pipe 30, and, at the tuyere 22, the flow of pulverized coal 3 can be passed through at a distance from the surface of the tuyere 22.

As a result, the amount of pulverized coal 3 passing over the surface of the tuyere 22 and the surface of the inner wall of the external pipe 30 a constituting the main body of the blow pipe (i.e., the surface of the inner wall of the blow pipe 30) is either eliminated or greatly reduced compared to a conventional structure not possessing an internal pipe 30 b, allowing for dramatic suppression of pulverized coal 3 slag adhesion.

In the blow-pipe structure according to the embodiment described above, it is preferable to provide a flow path resisting element 80 for reducing the cross-sectional area of the flow path in an outer circumferential flow path 30 d formed between the external pipe 30 a and the internal pipe 30 b and at a position near the outlet of the internal pipe 30 b. This flow path resisting element 80 allows for a greater flow rate within the internal pipe 30 b, where the flow path resistance is low, than within the external pipe.

As a result, hot air 2 flowing out of the external pipe 30 a flows in the direction of the axial center of the internal pipe 30 b, i.e., in the direction of the center of the flow path of the blow pipe 30, thus impeding the flow of the pulverized coal 3 introduced into the internal pipe 30 b in the direction of the external pipe 30 a, where it is desirable to prevent slag adhesion.

The flow path resisting element 80 described above is a member that projects from the surface of the inner wall of the external pipe 30 a or the outer wall of the internal pipe 30 b, or, alternatively, from the surfaces of both the inner wall of the external pipe 30 a and the outer wall of the internal pipe 30 b, thereby reducing the cross-sectional area of the flow path. There is no particular limitation upon the cross-sectional shape thereof. However, if a wedge-shaped projecting member, such as, for example, a flow path resisting element 80 comprising a slanted surface 81 that reduces the cross-sectional area of the flow path from the upstream side of the flow direction toward the downstream side, is provided on the surface of the inner wall of the external pipe 30 a, the slanted surface 81 will direct hot air 2 flowing through the outer circumferential flow path 30 d in the direction of the center of the tuyere 22, thereby directing the flow of pulverized coal 3 in the direction of the center of tuyere 22, and thus further suppressing the adhesion of slag from the pulverized coal 3.

The blow-pipe structure described above is preferably provided with a nitrogen injection pipe 90 for supplying nitrogen into the interior of the internal pipe 30 b. This nitrogen injection pipe 90 is used to introduce nitrogen gas into the hot air 2 flowing through the internal pipe 30 b as necessary, such as when it is desirable to alter the operating conditions of the internal pipe 30 b and the external pipe 30 a.

Accordingly, introducing nitrogen into the internal pipe 30 b reduces the temperature of the hot air, thus allowing the temperature of the hot air 2 to be reduced to or below the slag melting point. In other words, the nitrogen injection pipe 90 allows the temperature of the hot air with the internal pipe 30 b to be adjusted and the oxygen concentration to be reduced through the injection of nitrogen, thereby allowing for adjustment to an environment in which the pulverized coal 3 cannot easily combust.

The blow-pipe structure described above is preferably provided with an oxygen injection pipe 91 for supplying oxygen into the external pipe 30 a, i.e., into the outer circumferential flow path 30 d. This oxygen injection pipe 91 is used to introduce oxygen into the hot air 2 flowing through the external pipe 30 a as necessary, such as when it is desirable to alter the operating conditions of the internal pipe 30 b and the external pipe 30 a.

Accordingly, hot air 2, the oxygen concentration of which has been increased by injecting oxygen into the external pipe 30 a, is mixed with the pulverized coal 3 introduced into the internal pipe 30 b near the inlet of the tuyere 22, thereby allowing for rapid combustion of the pulverized coal 3. Accelerating combustion in this way increases the temperature of the hot air 2, thus further accelerating the combustion of the pulverized coal 3.

The process of adjusting the oxygen concentration of the hot air 2 will now be specifically described using an example.

Hot air 2 supplied from the header pipe 41 is set, for example, to an oxygen concentration of 21 vol %. In order to ensure combustion after convergence with the pulverized coal 3, oxygen is injected into the external pipe 30 a from the oxygen injection pipe 91 to enrich the oxygen concentration to 25 to 50 vol %, preferably 30 to 35 vol %.

As a result, the combustion rate of the pulverized coal 3 is reduced within the internal pipe 30 b, where the oxygen concentration is relatively lower than in the external pipe 30 a, allowing slag adhesion in the internal pipe 30 b to be suppressed. The hot air 2 and pulverized coal 3 flowing within the internal pipe 30 b then converge with the oxygen-enriched hot air 2 flowing in from the external pipe 30 a, thereby increasing the combustion rate of the pulverized coal 3 due to the increase in the oxygen concentration, and allowing for complete combustion of the pulverized coal 3 constituting the coal being injected into the main blast furnace body 20 within the raceway.

In addition to the adjustment of the oxygen concentration in this way, nitrogen may concurrently be introduced into the internal pipe 30 b to adjust the temperature of the hot air within the internal pipe 30 b to or below the ash melting point according to the form of the pulverized coal 3.

Thus, in accordance with the blow-pipe structure of the embodiment described above, there is provided an internal/external double pipe structure in which the internal pipe 30 b is provided within the external pipe 30 a continuing from the header pipe 41 to the tuyere 22, and the pulverized coal outlet 31 a of the lance 31 for introducing pulverized coal 3 opens to the interior of the internal pipe 30 b, thereby separating the flow of pulverized coal 3 from the surface of the tuyere 22 and the inner wall of the blow pipe 30, impeding the adhesion of slag from the pulverized coal 3.

This allows slag adhesion to be suppressed in the blow-pipe structure using a simple internal/external double pipe structure, even if the softening point of the pulverized coal 3 is not adjusted. As a result, the maintenance interval of the blow pipe 30 can be extended, for example, to the wear lifespan of the tuyere 22.

The component that is contained in the slag produced by the pulverized coal 3 described above and is melted by the hot air 2 or the heat produced by the combustion of the pulverized coal 3, i.e. the low-melting point slag component, has an ash melting point of roughly 1,100 to 1,300° C. when hot air 2 of roughly 1,200° C. is used. A low-melting point slag component of this sort is also contained in modified coal produced by modifying low-grade coal, such as sub-bituminous coal or lignite, used as the feedstock coal for the pulverized coal 3 via drying, dry distillation, or the like, but, by using the blow-pipe structure of the embodiment, pulverized coal 3 produced by modifying a low-grade feedstock coal can be used as an auxiliary fuel.

The present invention is not limited to the embodiment described above, and various modifications may be made thereto, as appropriate, within the scope of the invention.

REFERENCE SIGNS LIST

-   1 Feedstock -   2 Hot air -   3 Pulverized coal (modified coal) -   4 Carrier gas -   5 Pig iron (molten iron) -   10 Metered feedstock feeder -   20 Main blast furnace body -   21 Furnace apex hopper -   22 Tuyere -   30 Blow pipe -   30 a External pipe -   30 b Internal pipe -   30 c Internal pipe outlet -   30 d Outer circumferential flow path -   31 Injection lance (lance) -   31 a Pulverized coal outlet -   40 Hot air feeder -   41 Header pipe -   50 Pulverized coal producing device -   60 Cyclone separator -   70 Storage tank -   80 Flow path resisting element -   81 Slanted surface -   90 Nitrogen injection pipe -   91 Oxygen injection pipe 

1. A blow-pipe structure attached to a tuyere for a main blast furnace body that produces pig iron from iron ore, the blow-pipe structure injecting pulverized coal as an auxiliary fuel along with hot air, slag from the pulverized coal containing a component that is melted by the hot air and/or heat from the combustion of the pulverized coal combustion heat; the structure being an internal/external double pipe structure in which an internal pipe that continues from a header pipe, which supplies the hot air, to the vicinity of a tuyere and opens is provided inside an external pipe that continues from the header pipe to the tuyere, and a pulverized coal outlet of an injection lance for introducing the pulverized coal opens to the interior of the internal pipe.
 2. The blow-pipe structure according to claim 1, wherein a flow path resisting element is provided at a position in a flow path formed between the external pipe and the internal pipe and near the outlet of the internal pipe.
 3. The blow-pipe structure according to claim 1, wherein a nitrogen injection pipe for supplying nitrogen to the internal pipe is provided.
 4. The blow-pipe structure according to claim 1, wherein an oxygen injection pipe for supplying oxygen to the external pipe is provided.
 5. The blow-pipe structure according to claim 2, wherein a nitrogen injection pipe for supplying nitrogen to the internal pipe is provided.
 6. The blow-pipe structure according to claim 2, wherein an oxygen injection pipe for supplying oxygen to the external pipe is provided.
 7. The blow-pipe structure according to claim 3, wherein an oxygen injection pipe for supplying oxygen to the external pipe is provided. 